The invention relates to a friction lining mixture for a friction material, in particular for brake and clutch linings, the mixture comprising metal fibers and/or powders, functional fillers, lubricants, and organic compounds.
Such friction materials are needed for example for brake and clutch linings, for example for use in motor vehicles, rail vehicles or also in wind power plants. In addition, there is a multiplicity of other applications for such friction materials. Known friction material recipes generally have the following schematic composition:                metallic fibers and/or powder        functional fillers (e.g. glass fibers for reinforcement, metal oxides as friction modifiers, etc.)        solid lubricants        organic compounds (resins, rubber, fibers, etc.)        
Besides the technical requirements on friction material development such as typically the improvement of the performance capability, durability and comfort characteristics, the demands concerning environmental protection made on friction material development become more and more important.
From EP 0 654 616 B1 a friction lining mixture for brake and clutch linings is known, which comprises tin sulfides instead of the antimony sulfides customary until then to reduce the susceptibility to cracking of the friction partner. The use of tin sulfides in the friction lining mixture instead of the antimony sulfides customary until then is supposed to reduce the susceptibility to surface cracks of the friction partner occurring at high peak temperature loads.
According to DE-C1 153 670, the use of molybdenum, antimony, lead, zinc, cadmium and tin sulfides in friction lining mixtures is known.
DE-AS 1 150 918 discloses a method for producing a ceramic friction body for brakes and clutches wherein a dry mixture of 20 to 50 parts by weight of natural or synthetic inorganic fibers, 20 to 50 parts by weight of a low-melting glass frit of borates, silicates, phosphates or a mixture thereof, 10 to 40 parts by weight of a metal powder mixture, with the metal consisting of iron or ferrous metals, copper, bronze, brass and/or zinc, and 0 to 15 parts by weight of powdered graphite and/or a powdered sulfide of molybdenum, antimony, lead, tin, zinc or cadmium or powdered boron nitrides is plasticized, pressed into formed pieces with a pressure of about 1000 bar, dried at about 200° C., and then baked in air in a firing range that is between 550 and 650° C.
EP 0 093 673 B1 describes a friction lining mixture based on iron. Besides 72 to 85 percent by weight of powdered iron the friction lining mixture described there comprises 3 to 14 percent by weight of graphite, 2 to 12 percent by weight of coke, 3 to 10 percent by weight of a low-melting material such as for example tin, and up to 3 percent by weight of friction-modifying additives. In the production of the brake lining from this mixture, the iron and tin melt into an alloy with formation of a matrix in which the graphite, the coke and the additive are embedded in a relatively fixed position. The ratio of iron powder to tin should be about 12 to 1.
From EP 1 482 204 B1 a friction lining mixture comprising fibers, binder and filler is known. The fibers are mixtures of bronze fibers and inorganic or organic fibers. The bronze fibers are produced by subjecting them together with tin sulfides and metallic tin powder to a vibration cutting process.
The presence of copper, for example in bronze, in friction lining mixtures is necessary for performance, wear characteristics as well as durability (dust emission) and comfort.
EP 1 681 489 discloses a friction lining mixture comprising a phenolic resin as binder, in which between 1 and 10 percent by volume of iron fibers are embedded. The friction lining mixture further comprises between 1 and 5 percent by volume of aluminum, zinc, tin or mixtures thereof and about 4 percent by volume of antimony sulfide. Tin can be used in powder form or as fiber, the particles of the tin powder having a nominal diameter of about 1.5 mm. The friction lining mixture is free of copper.
US 2009/0064896 A1 discloses a friction lining mixture in which in situ formation of tin sulfide is supposed to take place. For this, the friction lining mixture comprises a sulfur source, typically iron(II) disulfide, a tin source, typically colloidal tin(IV) oxide. The iron disulfide particles can be coated with the tin oxide. The mixture can further comprise a reducing agent such as graphite. The reducing agent reduces tin oxide to metallic tin, which in turn can be reacted with the sulfur source to tin sulfide. Tin sulfide is formed during the braking process at temperatures of 600 to 900° C.